In general, a pressure-reducer (regulator) has a valve located between a primary port to which high pressure gas flows in and a secondary port for supplying gas to the outside. The valve is opened and closed so that the pressure (primary pressure) of high-pressure gas flowing into the primary port is reduced to a secondary pressure before the gas is supplied to the outside.
Such pressure reducers include piston type pressure reducers (for example, see Japanese Laid-Open Patent Publication No. 2004-192462). A piston type pressure reducer has a cylinder located downstream of a valve and a piston slidably accommodated in the cylinder. The piston separates a decompression chamber and a pressure adjusting chamber from each other. The valve is opened or closed based on the movement of the piston in accordance with the difference between the force received by the pressure adjusting chamber and the force received by the decompression chamber.
In such a piston type pressure reducer, a seal member is provided on the outer circumferential surface of the piston for sealing the decompression chamber and the pressure adjusting chamber from each other to maintain the hermeticity. In many cases, an O-ring is used as such a seal member.
In recent years, to increase storage capacity of hydrogen tanks used for fuel cell vehicles, the pressure in these tanks are more and more increased (for example, to 70 MPa). Accordingly, the pressure receiving surface of the above described piston, or the surface exposed to the decompression chamber, and the seal member receive extremely high gas pressure. To obtain a sufficient sealing performance of an O-ring in a conventional pressure reducer, the compressibility of the O-ring needs to be inevitably significantly high. As a result, due to an increased friction between the O-ring and the inner circumferential surface of the cylinder, the movement of the piston is hindered.